1. Field of the Invention
The present invention relates to a method for pulling a silicon single crystal which has a monocrystalline solid seed crystal of silicon being brought into contact with molten silicon material and an interface being formed between solid seed crystal and molten material, and the molten silicon material being caused to solidify with the formation of a thin-necked crystal and a cylindrical single crystal. The method is one wherein, during the pulling of the thin-necked crystal, it is ensured that the ratio V/G(r) is above a constant C.sub.crit having the value 1.3*10.sup.-3 cm.sup.2 /Kmin, with V being the pulling rate, with G(r) being the axial temperature gradient at the interface and r being the radial distance from the center of the thin-necked crystal.
2. The Prior Art
The most frequently used methods for pulling a single crystal by solidifying molten material are the Czochralski method (CZ method) and the float zone method (FZ method). These methods are described, for example, in Semiconductor Silicon Crystal Technology by F. Shimura (Academic Press, London 1988, pages 124-127, 130-131 and 135) with reference to the example of producing silicon single crystals.
The production of silicon single crystals using the aforementioned methods is divided into several phases. After polycrystalline silicon (polysilicon) has been melted, a seed crystal of given crystal orientation is brought into contact with the melt. Then a 2-3 mm wide and several centimeters long thin-necked crystal is pulled, whose diameter is subsequently increased to the target diameter of the silicon single crystal to be produced. The phase of pulling the thin-necked crystal is used to eliminate dislocations present in the seed crystal and is carried out in the prior art according to Dash's principle (W. C. Dash, J. Appl. Phys. 29 (1958), 736-737). If, during this phase, the dislocations are not successfully eliminated, then it is not subsequently possible to produce a dislocation-free silicon single crystal.
Such silicon single crystals are the basic material for electronic components whose functional capacity depends, for example, on the freedom of the basic material from defects. Thus there is the requirement for defect-free and therefore also dislocation-free single crystals as a result.
In relation to the production of silicon single crystals, a study has been published (E. Dornberger and W. v. Ammon, Journal of the Electrochem. Soc., Vol. 143, No. 5, May 1996, 1648-1653). This study links the occurrence of particular crystal defects when pulling a single crystal with particular parameters which play a role in the pulling of the single crystal.